Analytical and Bioanalytical Chemistry (v.356, #7)

Interlaboratory studies to improve the quality of mercury determination in seawater by P. Quevauviller; K. J. M. Kramer; E. M. van der Vlies; W. Dorten; B. Griepink (411-415).
Determinations of pollutants in various matrices are routinely performed by a number of organizations for monitoring contamination levels of the marine environment. Projects for improving the quality of determinations of trace metals in seawater have been successfully concluded within the scope of the BCR-Programme (now renamed Standards, Measurements and Testing Programme) of the European Commission; however, the determination of total mercury could not be considered at this stage both because of the poor analytical performances observed and the unsuitability of the containers (polyethylene) used for the seawater certified reference material (CRM 579). A specific project has therefore been organized to improve the state of the art of Hg determination in seawater and to investigate the best way of storing a candidate CRM. Two interlaboratory studies have been concluded and a certification campaign has now started. The materials have been collected in the Southern Bight of the North Sea, carefully prepared (filtered and acidified) and their homogeneity and stability were verified. This paper presents the results of the two interlaboratory studies.

Determination of total chromium in Marine Sediment Reference Material BCSS-1 by J. Liu>; R. E. Sturgeon; V. J. Boyko; S. N. Willie (416-419).
The determination of Cr in National Research Council of Canada Marine Sediment Reference Material BCSS-1 is addressed. Mixed acid digestions utilizing HF, HClO4 and HNO3 were investigated. Single microwave assisted digestions in closed vessels at medium pressures (8 bar) were inappropriate (80% recovery). Double digestion at moderate pressure and digestions at high pressure (70 bar) or lengthy open-beaker hot plate dissolutions resulted in 93±5% recovery of certified Cr content. Flame atomic absorption and inductively coupled plasma atomic emission spectrometry were used for quantitation. In all cases, the method of standard additions was necessary to eliminate the approximately 10% enhancement in re- sponce relative to unmatched standards. Compared to a certified content of 123±7 μg/g (mean and standard deviation), values of 116±6 were obtained using an open beaker digestion; 114±5 using a double microwave digestion at 8 bar; 113±2 for microwave digestion at high pressure and 111±4 at high pressure (81 bar) with triple microwave digestion in a Parr bomb. No acid dissolution procedure is adequate for Cr in this sample although recovery of total Cr is complete from National Institute of Standards and Technology Buffalo River Sediment (SRM 2704).

Equilibrium distribution coefficients, Kd, are presented for some elements in hydrochloric acid using the phosphonated polystyrene ion exchange resin Purolite S-950. A few possible separations using this resin are demonstrated by elution curves and separations of synthetic mixtures of some elements (Ru, Rh, Mo, I, Li, Te, Si, Y).

The behaviour of Mo and some other elements on Ag MP-1 in alkaline medium was investigated. Equilibrium distribution coefficients, Kd, are presented for Mo on the anion exchangers AG 1-X2, AG 1-X4, AG 1-X8 and AG MP-1, and for some elements on AG MP-1 in alkaline medium. An anion exchange chromatographic separation of Mo from some of these elements is described and some results obtained with this method are reported.

Application of countercurrent chromatography to the purification of chemical reagents by T. A. Maryutina; B. Y. Spivakov; P. Tschöpel (430-434).
Countercurrent chromatography has been employed for the purification of solid chemical reagents, such as (NH4)2SO4, NH4HSO4, NH4F and NH4Cl from a number of most common metal impurities (Fe, Al, Zn, Cu, Co, Cd, Ni, Cr, Ca, Mg, K) in order to gain high-purity reagents. After evaporation these can be used for fusion decomposition purposes in trace analysis of various refractory materials (e.g. high tech ceramics). N,N-hexamethylenedithiocarbamic acid, 8-hydroxyquinoline, dibenzo-18-crown-6 and dicyclohexano-18-crown-6 were used as extracting reagents.

Flow-injection hydride generation and in situ concentration of As, Sb and Bi hydrides in graphite furnace atomic absorption spectrometry can be automated by means of a long-term stable trapping reagent replacing the Pd modifier. In a systematic study, carbide-forming elements (Zr, Nb, Ta, W) and noble metals (Ir, Ir/Mg, Pd/Ir) were investigated as stable adsorbers which require only a single application. Trapping temperature curves indicate high signals for trapping of As at 750–800 °C, Sb at 450–8000 °C and Bi at 100–500 °C on Zr-coated tubes. Ir- and Ir/Mg-coated tubes showed a high response for Sb and Bi at lower temperatures, but based on signal stability and reproducibility (over 400 trapping and atomization cycles tested) the better performance was found with the Zr-coated tubes. The radiotracers Sb-125 and Bi-207 were used to measure the hydride generation (>95% for both elements) and trapping efficiency (91% for Sb and 56% for Bi) on the Zr-coated tube. An adsorptive “carry-over effect” was observed with Sb and Bi but not with As, and trapping temperatures above 450 °C with Sb and 350 °C with Bi (the “critical temperatures”) can lead to errors in absorbance values. On a Zr-coated tube the characteristic mass was about 16 pg for As, 15 pg for Sb and 9 pg for Bi (peak height) and the detection limits (3 sigma) were about 0.015, 0.010 and 0.027 ng, respectively, with a 1 ml sample loop. The method was tested by the determination of the elements in NIST low-alloy steel certified reference materials.

High-field proton nuclear magnetic resonance (1H-NMR) spectroscopy was applied to the analysis of nitroaromatics and nitramines in ammunition waste water. The 1H-chemical shifts data of a variety of reference compounds are presented. Three groundwater samples, taken near the former ammunition plant Elsnig (Saxony), were analysed by high-performance liquid chromatography (HPLC) and by proton nuclear magnetic resonance spectroscopy. The results of HPLC and NMR analyses are compared and discussed.

A selective, sensitive and reliable voltam- metric method for the simultaneous determination of MoS2- 4 and MoO2- 4 has been developed. The reduction of HgMoS4 at −0.43 V and the reduction of Mo as complex of MoO2-oxine2 at −0.63 V in acetate buffer at pH 4.9 are utilized for the simultaneous determination by differential pulse cathodic stripping voltametry (DPCSV). Cadmium and lead form complexes with MoS2- 4, but do not interfere with the determination. The limit of detection is 0.59 μg/l Mo for MoS2- 4 and 1.8 μg/l Mo for MoO2- 4. The R.S.D at a concentration level of 20 μg/l is 4.7% for MoO2- 4 and 3.6% for MoS2- 4. The method is applied to spiked blood plasma samples for the determination of free tetrathiomolybdates and molybdates. Additionally, labile tetrathiomolybdates and molybdates can be determined in spiked blood plasma after treatment of the sample with 0.15 mol/l KCN and ultrafiltration.

An automated procedure for sample work-up and preparation of calibration standards for HPLC analyses is presented. The equipment consisting of a benchtop workstation and a conventional HPLC system was used to analyze aqueous solutions containing Iotetrol, a contrast medium. The four rotamers of the test compound were separated using the stationary phase Hypercarb S and by elution with tetrahydro-furan/water 3:97 (w/w). The analytical procedure was characterized with respect to sensitivity, selectivity, linearity of the detector response, accuracy, precision and carry-over effect. The use of the workstation yielded excellent data with respect to accuracy (102%) and precision (1%). At the stage of method development, the influence of post-column photoderivatization on the detectability of the analyte was investigated. As a result, a bathochromic shift of the UV absorbance maximum and the considerable intensification of the rudimentary fluorescence properties of the Iotetrol molecule were observed. The automatization saved a considerable amount of man-hours (ca. 25%).

The titration of a multicomponent mixture can be described either with de Levie’s integral representation [1] or with Moisio’s and Heikonen’s derivative representation [2]. In the latter method an experimental titration curve is numerically differentiated and the computations are based on the buffer capacity. Numerical calculations demonstrate that the results of these two methods coincide very well.